The present invention relates to the use of time delay integration sensors and, in particular, the use of time delay integration sensors for inspecting circuit patterns.
Many techniques exist to inspect circuit patterns on integrated circuit chips. One such technique involves the use of fluorescence to inspect such patterns. In particular, when certain types of which circuits are composed of organic and inorganic substances are illuminated with certain wave lengths of light, the organic portions fluoresce while the inorganic portions do not, thereby providing a high contrast image for inspection. However, the fluorescence is such that for an image of the chip to be adequately captured by a sensor, that sensor must be exposed for a minimum period of time. This minimum period of time for exposure can limit the rate at which chips move pass the sensor. To increase throughput while maintaining an acceptable degree of quality in the captured images the prior art has provided for the use of time delay integration (TDI) sensors.
A typical TDI sensor is generally illustrated in FIG. 5. TDI sensors typically include a two dimensional array of photo sites arranged in rows and columns. At a defined time, the charges in the photo sites of a column are moved, in mass, to the photo sites in the adjacent column as illustrated by arrow A. The rate at which the charges are moved from column to column is called the clock rate. Concurrent with the shifting of the charges in the columns of the TDI sensor, the laser stripe, or circuit chip, moves at the same rate such that the same part of the circuit chip is continuously integrated by subsequent columns of photo sites. By shifting the columns together with the continuous movement of the chip being inspected, prior art systems have increased through put while maintaining acceptable images.
Typical fluorescence inspection systems include a pair of lasers which continuously illuminate the surface. Two lasers are used to eliminate shadows on the circuit chip. Because the lasers are continuous, their power must be decreased to avoid damaging the circuit chip. By de-powering the laser the amount of fluoresce is correspondingly decreased. As described above, the circuit chip is positioned on a stage which moves synchronously with the shifting columns of the TDI sensors. However, there exists a need to improve the quality of images captured in such systems.
The present invention provides for a circuit chip inspection device and method. In its preferred embodiment the inventive device and method are used for fluorescent inspection of circuit chips.
The circuit chip inspection device is for inspecting a circuit chip where the circuit chip is on a movable stage with the stage moving substantially continuously along an axis at a defined rate. The circuit chip inspection device includes a pulsed laser, a time delay integration (TDI) sensor and a controller. The pulsed laser is operative to emit a stripe of laser pulses at controlled intervals with the pulses being directed toward the circuit chip as to illuminate the circuit chip. The TDI sensor captures an image of the circuit chip. The TDI sensor is defined by an array of photo sites having at least one row of photo sites and a plurality of columns of photo sites. Each photo site is chargeable and the sensor is operative to transfer a charge from column to column at a predefined rate. The TDI sensor and movable stage are coordinated such that the charges are being clocked from column to column at the same rate at which the stage is moving. The controller is connected to the pulsed laser and configured to activate the laser in synchronization with the rate at which the TDI sensor transfers charges from column to column such that the laser is activated when the charge resides in a column and the laser is deactivated when the charge is being transferred from column to column.
Preferably, the controller can be connected to the movable stage and to the TDI sensor; the controller operative in determining whether the stage is moving at the same rate as the rate at which the charges are being shifted from column to column in the TDI sensor with the controller being operative to adjust the rate at which the stage is moving.
The controller can preferably measure the movement of the stage in units of pixels which correspond to the size of the photo sites on the TDI sensor. The controller can then be operative to activate the laser when it determines that the stage has moved a half of a pixel.
The method for inspecting circuit chips according to the present invention is as follows. The circuit chip is on a movable stage with the stage moving substantially continuously along an axis at a defined rate. The method includes imaging the circuit and pulsing a stripe of lasers at the circuit. The circuit is imaged with a time delay integration (TDI) sensor, the TDI sensor defined by an array of photo sites, having at least one row of photo sites and a plurality of columns of photo sites. Each photo site is chargeable and the TDI sensor is operative to transfer a charge from column to column at a predefined rate. The TDI sensor and movable stage are coordinated such that the charges are being clocked from column to column at the same rate at which the stage is moving. The laser stripe is pulsed toward the circuit chip as to illuminate the circuit chip where the laser pulses are in synchronization with the rate at which the sensor transfers charges from column to column such that the laser is activated when the charge resides in a column and the laser is deactivated when the charge is being transferred from column to column.
Other applications of the present invention will become apparent to those skilled in the art when the following description of the best mode contemplated for practicing the invention is read in conjunction with the accompanying drawings.